The present application claims priority under 35 U.S.C. xc2xa7 119 of Japanese Application No. 2001-362375, filed Nov. 28, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to an episulfide compound, a method for producing the same, and an optical product made with the same. Generally, the invention relates to an episulfide compound that may give optical materials having a high refractive index and a high Abbe""s number and having excellent heat resistance and transparency, to a method for producing the same, and to an optical product made with the same.
2. Background of the Invention
Plastics are used for various optical applications these days, for example, for lenses and others, as being lightweight, difficult to break, and easily colored when compared with glass. Optical plastic materials include poly(diethylene glycol bisallylcarbonate) (CR-39) and poly(methyl methacrylate). These plastics, however, have a refractive index of 1.50 or less. Therefore, for example, when they are used for lens materials, the lenses produced need to be thicker for increased power, and they lose the advantage of being lightweight. In particular, powerful concave lenses are thick at their periphery, and are therefore unfavorable as causing birefringence and chromatic aberration. For spectacles, such thick lenses are often not aesthetic. To obtain thin lenses, materials with higher refractive index may be used. In general, the Abbe""s number of glass and plastics decreases with the increase in their refractive index, and, as a result, their chromatic aberration increases. Accordingly, plastic materials having a high refractive index and a high Abbe""s number are desired.
Plastic materials proposed as having such properties include, for example, (1) polyurethanes obtained through addition-polymerization of a polythiol having bromine in the molecule and a polyisocyanate (Japanese Patent Laid-Open No.164615/1983); and (2) polythiourethanes obtained through addition-polymerization of a polythiol and a polyisocyanate (Japanese Patent Publication No. 58489/1992 and Japanese Patent Laid-Open No.148340/1993). For the starting material, polythiol for the polythiourethanes of above (2), may be branched polythiols having an increased sulfur content (Japanese Patent Laid-Open Nos. 270859/1990 and 148340/1993), and polythiols into which is introduced a dithiane structure for increasing their sulfur content (Japanese Patent Publication No. 5323/1994 and Japanese Patent Laid-Open No.118390/1995). Other plastic materials proposed as having such properties include (3) polymers of an alkyl sulfide having a polymerization-functional group, episulfide (Japanese Patent Laid-Open Nos. 71580/1997 and 110979/1997).
However, though their refractive index is increased a little, the polyurethanes of above (1) still have a low Abbe""s number and have some other drawbacks in that their lightfastness is poor, their specific gravity is high and, therefore, they are not lightweight. Of the polythiourethanes (2), those for which the starting polythiol used has a high sulfur content have an increased refractive index of from about 1.60 to 1.68, but their Abbe""s number is lower than that of optical inorganic glass having a refractive index on the same level. Therefore, they still have a problem in that their Abbe""s number must be increased more. On the other hand, one example of the alkyl sulfide polymers (3) having an Abbe""s number of 36 has an increased refractive index of 1.70. The lenses obtained by using this polymer can be extremely thin and lightweight. However, plastic materials with high Abbe""s number and refractive index are still desired.
The present invention has been made to address the problems noted above. The present invention provides compounds that may give optical materials having a high refractive index and a high Abbe""s number and having excellent heat resistance and transparency, a method for producing the same, and an optical product made with the same.
The present inventors have determined that compounds of 1,3,5-trithiane (hereinafter abbreviated as xe2x80x9ctrithianexe2x80x9d) with an episulfide derivative bonded thereto are useful in solving the above-noted problems, and that the compounds may be efficiently produced in a specific method. Specifically, the invention provides an episulfide compound represented by the general formula (1): 
wherein EP represents 
and n is an integer of from 0 to 2. The invention also provides a method for producing an episulfide compound represented by the general formula (1) by reacting a mercapto group-containing episulfide compound with 2,4,6-trimethylene-1,3,5-trithiane.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the various embodiments of the present invention only. In this regard, no attempt is made to show details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
Unless otherwise stated, a reference to a compound or component, includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
The episulfide compound of the invention is represented by the general formula (1) mentioned below, from which it is seen that the compounds have three, optionally identical, episulfide-containing substituents bonded to the trithiane ring thereof. 
wherein EP represents 
and n is an integer of from 0 to 2.
The trithiane ring of the episulfide compound represented by the general formula (1) has a high sulfur content, in which the atomic refraction is high and which therefore significantly increases the refractive index of the polymers obtained by using the episulfide compound of the invention. In addition, the ethylene sulfide chain to be formed through ring-cleavage polymerization of the episulfide compound also contributes toward increasing the refractive index of the polymers. In general, the Abbe""s number of amorphous materials is apt to decrease with the increase in the refractive index thereof. One problem with polymers having high sulfur content is that the electron resonance of sulfur is remarkable, therefore often significantly reducing the Abbe""s number. However, the episulfide compounds of the invention are free from this problem. Another cause of the increase in the refractive index is the decrease in the molar volume thereof. This is often seen in polymers having a high crosslinking density and a strong intermolecular force. The episulfide compound of the invention has three polymerization-functional groups, and the refractive index of its polymers is increased especially by the former effect. In the general formula (1), the increase in the number n lowers the sulfur content and the crosslinking density, therefore giving polymers having a reduced refractive index. Accordingly, n is generally in a range of from 0 to 2. In addition, since the glass transition temperature (Tg) of the polymers obtained by using the episulfide compound of the invention lowers with the increase in n in the general formula (1), n is generally in a range of from 0 to 2 in order to obtain polymers having good heat resistance.
For example, the episulfide compound represented by the general formula (1) of the invention includes 2,4,6-tris(epithiomethylthiomethyl)-1,3,5-trithiane, 2,4,6-tris(epithioethylthiomethyl)-1,3,5-trithiane, and 2,4,6-tris(epithiopropylthiomethyl)-1,3,5-trithiane.
These episulfide compounds of the invention may be efficiently produced according to the method of the invention by reacting 2,4,6-trimethylene-1,3,5-trithiane having a methylene group introduced into its 2,4,6-positions, with a mercapto group-containing episulfide compound at the methylene group of the trithiane through ene-thiol reaction.
The mercapto group-containing episulfide compound includes 3-mercaptopropene sulfide, 4-mercaptobutene sulfide, and 5-mercaptopentene sulfide. For example, 3-mercaptopropene sulfide may be prepared according to the method described in F. P. Doyle et al., Journal of Chemical Society, p. 2660 (1960).
The method for producing the episulfide compound of the invention may comprise the following steps:
(a) reacting chloroacetaldehyde with hydrogen sulfide to obtain 2,4,6-tris(chloromethyl)-1,3,5-trithiane;
(b) adding a base to the product obtained in step (a) to remove hydrogen chloride to obtain 2,4,6-trimethylene-1,3,5-trithiane; and
(c) reacting the 2,4,6-trimethylene-1,3,5-trithiane with 3-mercaptopropene sulfide/4-mercaptobutene sulfide/5-mercaptopropentene sulfide in the presence of a radical generator to obtain the episulfide compound.
One typical example of the method for producing an episulfide compound of the invention, 2,4,6-tris(epithiomethylthiomethyl)-1,3,5-trithiane (a compound of the general formula (1) wherein n is 0), is shown as Scheme 1 mentioned below. An aqueous 40 wt. % chloroacetaldehyde solution is dissolved in 70 wt. % sulfuric acid, and hydrogen sulfide is introduced thereinto at xe2x88x9220 to 40xc2x0 C. for 2 to 100 hours to give 2,4,6-tris(chloromethyl)-1,3,5-trithiane. Alternatives to sulfuric acid as the acidic solvent include any of 60/40 (v/v) 95 wt. % sulfuric acid-acetic acid, or hydrogen sulfide-saturated acetic acid, ether, or 95 wt. % ethanol. To the resulting methanol solution of the thus-formed chlorine compound is added potassium hydroxide with which the chlorine compound is processed at xe2x88x9210 to 40xc2x0 C. for 0.5 to 10 hours for removal of hydrogen chloride from it to give 2,4,6-trimethylene-1,3,5-trithiane. This is thermally reacted with 3-mercaptopropene sulfide at 0 to 100xc2x0 C. for 6 to 100 hours in the presence of a radical generator (described below), to obtain the intended product, 2,4,6-tris(epithiomethylthiomethyl)-1,3,5-trithiane.
The radical generator may be any of azobisbutyronitrile, benzoyl peroxide, or bis(cyclohexylcarbonyl) peroxide.
Alternatives to 3-mercaptopropene sulfide as the mercapto group-containing episulfide compound include 4-mercaptobutene sulfide and 5-mercaptopentene sulfide, and these give 2,4,6-tris(epithioethylthiomethyl)-1,3,5-trithiane and 2,4,6-tris(epithiopropylthiomethyl)-1,3,5-trithiane, respectively. 
wherein EP represents 
and Me is a methyl group.
Next, are described optical materials obtained by using the episulfide compound of the invention. The episulfide compound represented by the general formula (1) is a component, and it may be used either singly or in admixture of two or more thereof. Further, the episulfide compound may contain any other optional component including other episulfide compounds, epoxy compounds, and homopolymerizable vinyl monomers, for suitably improving the properties of the polymers to be obtained.
Examples of the optional episulfide compounds are linear organic compounds such as bis(xcex2-epithiopropylthio)methane, 1,2-bis(xcex2-epithiopropylthio)ethane, 1,3-bis(xcex2-epithiopropylthio)propane, 1,2-bis(xcex2-epithiopropylthio)propane, 1-(xcex2-epithiopropylthio)-2-(xcex2-epithiopropylthiomethyl)propane, 1,4-bis(xcex2-epithiopropylthio)butane, 1,3-bis(xcex2-epithiopropylthio)butane, 1-(xcex2-epithiopropylthio)-3-(xcex2-epithiopropylthiomethyl)butane, 1,5-bis(xcex2-epithiopropylthio)pentane, 1-(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)pentane, 1,6-bis(xcex2-epithiopropylthio)hexane, 1-(xcex2-epithiopropylthio)-5-(xcex2-epithiopropylthiomethyl)hexane, 1-(xcex2-epithiopropylthio)-2-[(2-xcex2-epithiopropylthioethyl)thio]ethane, and 1-(xcex2-epithiopropylthio)-2-[[2-(2-xcex2-epithiopropylthioethyl)thioethyl]thio]ethane; branched organic compounds such as tetrakis(xcex2-epithiopropylthiomethyl)methane, 1,1,1-tris(xcex2-epithiopropylthiomethyl)propane, 1,5-bis(xcex2-epithiopropylthio)-2-(xcex2-epithiopropylthiomethyl)-3-thiapentane, 1,5-bis(xcex2-epithiopropylthio)-2,4-bis(xcex2-epithiopropylthiomethyl)-3-thiapentane, 1-(xcex2-epithiopropylthio)-2,2-bis(xcex2-epithiopropylthiomethyl)-4-thiahexane, 1,5,6-tris(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)-3-thiahexane, 1,8-bis(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-4,5-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-4,4-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-2,4,5-tris(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-2,5-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,9-bis(xcex2-epithiopropylthio)-5-(xcex2-epithiopropylthiomethyl)-5-[(2-xcex2-epithiopropylthioethyl)thiomethyl]-3,7-dithianonane, 1,10-bis(xcex2-epithiopropylthio)-5,6-bis[(2-xcex2-epithiopropylthioethyl)thio]-3,6,9-trithiadecane, 1,11-bis(xcex2-epithiopropylthio)-4,8-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, 1,11-bis(xcex2-epithiopropylthio)-5,7-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, and 1,11-bis(xcex2-epithiopropylthio)-5,7-[(2-xcex2-epithiopropylthioethyl)thiomethyl]-3,6,9-trithiaundecane, 1,11-bis(xcex2-epithiopropylthio)-4,7-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, and compounds derived therefrom by substituting at least one hydrogen of the episulfide group with a methyl group; alicyclic organic compounds such as 1,3- and 1,4-bis(xcex2-epithiopropylthio)cyclohexanes, 1,3- and 1,4-bis(xcex2-epithiopropylthiomethyl)cyclohexanes, bis[4-(xcex2-epithiopropylthio)cyclohexyl]methane, 2,2-bis[4-(xcex2-epithiopropylthio)cyclohexyl]propane, bis[4-(xcex2-epithiopropylthio)cyclohexyl] sulfide, 2,5-bis(xcex2-epithiopropylthiomethyl)-1,4-dithiane, and 2,5-bis(xcex2-epithiopropylthioethylthiomethyl)-1,4-dithiane, and compounds derived therefrom by substituting at least one hydrogen of the episulfide group therein with a methyl group; and aromatic organic compounds such as 1,3- and 1,4-bis(xcex2-epithiopropylthio)benzenes, 1,3- and 1,4-bis(xcex2-epithiopropylthiomethyl)benzenes, bis[4-(xcex2-epithiopropylthio)phenyl]methane, 2,2-bis[4-(xcex2-epithiopropylthio)phenyl]propane, bis[4-(xcex2-epithiopropylthio)phenyl] sulfide, bis[4-(xcex2-epithiopropylthio)phenyl] sulfone, and 4,4xe2x80x2-bis(xcex2-epithiopropylthio)biphenyl, and compounds derived therefrom by substituting at least one hydrogen of the episulfide group with a methyl group. They may be used herein either singly or in admixture of two or more thereof. The amount to be used is generally from 0.01 to 50 mole % of the total amount of the episulfide compound represented by the general formula (1).
Examples of the optional epoxy compounds are phenolic epoxy compounds produced through condensation of polyhydric phenol compounds, such as hydroquinone, catechol, resorcinol, bisphenol A, bisphenol F, bisphenol sulfone, bisphenol ether, bisphenol sulfide, bisphenol A halides, and novolak resin, with epihalohydrins; alcoholic epoxy compounds produced through condensation of polyhydric alcohol compounds, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, trimethylolpropane trimethacrylate, pentaerythritol, 1,3- and 1,4-cyclohexanediols, 1,3- and 1,4-cyclohexanedimethanols, hydrogenated bisphenol A, bisphenol A-ethylene oxide adduct, and bisphenol A-propylene oxide adduct, with epihalohydrins; glycidyl ester-based epoxy compounds produced through condensation of polyhydric carboxylic acid compounds, such as adipic acid, sebacic acid, decanedicarboxylic acid, dimer acids, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, hexachloroendomethylene tetrahydrophthalic (xe2x80x9cHETxe2x80x9d) acid, nadic acid, maleic acid, succinic acid, fumaric acid, trimellitic acid, benzenetetracarboxylic acid, benzophenonetetracarboxylic acid, naphthalenedicarboxylic acid, and diphenyldicarboxylic acid, with epihalohydrins; amine-based epoxy compounds produced through condensation of primary amines, such as ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, bis(3-aminopropyl) ether, 1,2-bis(3-aminopropoxy)ethane, 1,3-bis(3-aminopropoxy)-2,2xe2x80x2-dimethylpropane, 1,2-, 1,3- and 1,4-bisaminocyclohexanes, 1,3- and 1,4-bisaminomethylcyclohexanes, 1,3- and 1,4-bisaminoethylcyclohexanes, 1,3- and 1,4-bisaminopropylcyclohexanes, hydrogenated 4,4xe2x80x2-diaminodiphenylmethane, isophoronediamine, 1,4-bisaminopropylpiperazine, m- and p-phenylenediamines, 2,4- and 2,6-tolylenediamine, m- and p-xylylenediamines, 1,5- and 2,6-naphthalenediamines, 4,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenyl ether, and 2,2-(4,4xe2x80x2-diaminodiphenyl)propane, or secondary amines, such as N,Nxe2x80x2-dimethylethylenediamine, N,Nxe2x80x2-dimethyl-1,2-diaminopropane, N,Nxe2x80x2-dimethyl-1,3-diaminopropane, N,Nxe2x80x2-dimethyl-1,2-diaminobutane, N,Nxe2x80x2-dimethyl-1,3-diaminobutane, N,Nxe2x80x2-dimethyl-1,4-diaminobutane, N,Nxe2x80x2-dimethyl-1,5-diaminopentane, N,Nxe2x80x2-dimethyl-1,6-diaminohexane, N,Nxe2x80x2-dimethyl-1,7-diaminoheptane, N,Nxe2x80x2-diethylethylenediamine, N,Nxe2x80x2-diethyl-1,2-diaminopropane, N,Nxe2x80x2-diethyl-1,3-diaminopropane, N,Nxe2x80x2-diethyl-1,2-diaminobutane, N,Nxe2x80x2-diethyl-1,3-diaminobutane, N,Nxe2x80x2-diethyl-1,4-diaminobutane, N,Nxe2x80x2-diethyl-1,6-diaminohexane, piperazine, 2-methylpiperazine, 2,5- and 2,6-dimethylpiperazines, homopiperazine, 1,1-di(4-piperidyl)methane, 1,2-di(4-piperidyl)ethane, 1,3-di(4-piperidyl)propane, and 1,4-di(4-piperidyl)butane, with epihalohydrins; alicyclic epoxy compounds such as 3,4-epoxycyclohexyl 3,4-epoxycyclohexanecarboxylate, vinylcyclohexane dioxide, 2-(3,4-epoxycyclohexyl)-5,5-spiro-3,4-epoxycyclohexanemetadioxane, and bis(3,4-epoxycyclohexyl) adipate; epoxy compounds produced through epoxydation of unsaturated compounds, such as cyclopentadiene epoxide, epoxidated soybean oil, epoxydated polybutadiene, and vinylcyclohexene epoxide; and urethane-based epoxy compounds obtained from the above-mentioned polyhydric alcohols or phenolic compounds with diisocyanates and glycidols. They may be used herein either singly or in admixture of two or more thereof. The amount to be used is generally from 0.01 to 50 mole % of the total amount of the episulfide compound represented by the general formula (1).
Examples of the optional, homopolymerizable vinyl monomers are compounds having an ester structure of acrylic or methacrylic acid with a monohydric or polyhydric alcohol, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, 2,2-bis[4-(acryloxyethoxy)phenyl]propane, 2,2-bis[4-(methacryloxyethoxy)phenyl]propane, 2,2-bis[4-(acryloxydiethoxy)phenyl]propane, 2,2-bis[4-(methacryloxydiethoxy)phenyl]propane, 2,2-bis[4-(acryloxypolyethoxy)phenyl]propane, 2,2-bis[4-(methacryloxypolyethoxy)phenyl]propane, trimethylolpropane triacrylate, trimethylol propane trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, bis(2,2,2-trimethylolethyl) ether hexaacrylate, and bis(2,2,2-trimethylolethyl) ether hexamethacrylate; allyl compounds such as allyl sulfide, diallyl phthalate, and diethylene glycol bisallylcarbonate; vinyl compounds such as acrolein, acrylonitrile, and vinyl sulfide; and aromatic vinyl compounds such as styrene, xcex1-methylstyrene, methylvinylbenzene, ethylvinylbenzene, xcex1-chlorostyrene, chlorovinylbenzene, vinylbenzyl chloride, paradivinylbenzene, and metadivinylbenzene. They may be used herein either singly or in admixture of two or more thereof. The amount to be used is generally from 0.01 to 20 mole % of the total amount of the episulfide compound represented by the general formula (1).
To the polymerizable composition that comprises the above-mentioned episulfide compound represented by the general formula (1) and optional components, if desired, is optionally added other additives, such as UV absorbent, antioxidant, discoloration inhibitor, and fluorescent dye for improving the weather resistance of the resulting polymers. Also if desired, catalysts may be used for improving the polymerization reactivity. Examples of the catalysts include, for example, amines, phosphines, quaternary ammonium salts, quaternary phosphonium salts, tertiary sulfonium salts, secondary iodonium salts, mineral acids, Lewis acids, organic acids, silicic acids, and tetrafluoroboric acid.
Using the episulfide compounds of the invention, optical materials can be produced, for example, according to the method mentioned below.
A uniform composition containing the above-mentioned polymerizable composition and other optional additives is first prepared, and this is cast into a glass or metal mold combined with a resin gasket, and heated and cured therein, according to a method of casting polymerization. If desired, the mold may be subjected to mold release or a mold releasing agent may be added to the composition, for facilitating good release of the molded resin from the mold. The polymerization temperature varies depending on the compounds to be used, but is generally from xe2x88x9220xc2x0 C. to +150xc2x0 C.; and the polymerization time is from about 0.5 to 72 hours. After having been thus polymerized and released from the mold, the polymer may be readily colored with an ordinary disperse dye in water or in an organic solvent. For facilitating the dyeing, a carrier may be added to the dye dispersion, or the dyeing bath may be heated. Though not limited thereto, the thus-obtained optical materials are especially favorable for optical products such as plastic lenses.
The episulfide compounds of the invention have three, episulfide group-containing reactive substituents bonded to the center trithiane ring, and are favorable for starting materials for optical materials. The optical materials obtained by using the episulfide compounds of the invention have a high refractive index and a high Abbe""s number, and have excellent heat resistance and transparency. Therefore, they are suitable for materials for optical products, for example, for lenses such as those for spectacles and cameras, and also for prisms, optical fibers, substrates for recording media such as optical discs and magnetic discs, as well as for color filters, IR-absorbing filters, etc.